sysdeps/ieee754/ldbl-128ibm/s_logbl.c

   1 /* s_logbl.c -- long double version of s_logb.c.
   2  * Conversion to IEEE quad long double by Jakub Jelinek, jj@ultra.linux.cz.
   3  */
   4
   5 /*
   6  * ====================================================
   7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   8  *
   9  * Developed at SunPro, a Sun Microsystems, Inc. business.
  10  * Permission to use, copy, modify, and distribute this
  11  * software is freely granted, provided that this notice
  12  * is preserved.
  13  * ====================================================
  14  */
  15
  16 /*
  17  * long double logbl(x)
  18  * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
  19  * Use ilogb instead.
  20  */
  21
  22 #include <math.h>
  23 #include <math_private.h>
  24 #include <math_ldbl_opt.h>
  25 #include <fix-int-fp-convert-zero.h>
  26
  27 long double
  28 __logbl (long double x)
  29 {
  30   int64_t hx, hxs, rhx;
  31   double xhi, xlo;
  32
  33   ldbl_unpack (x, &xhi, &xlo);
  34   EXTRACT_WORDS64 (hx, xhi);
  35   hxs = hx;
  36   hx &= 0x7fffffffffffffffLL;   /* high |x| */
  37   if (hx == 0)
  38     return -1.0 / fabs (x);
  39   if (hx >= 0x7ff0000000000000LL)
  40     return x * x;
  41   if (__glibc_unlikely ((rhx = hx >> 52) == 0))
  42     {
  43       /* POSIX specifies that denormal number is treated as
  44          though it were normalized.  */
  45       rhx -= __builtin_clzll (hx) - 12;
  46     }
  47   else if ((hx & 0x000fffffffffffffLL) == 0)
  48     {
  49       /* If the high part is a power of 2, and the low part is nonzero
  50          with the opposite sign, the low part affects the
  51          exponent.  */
  52       int64_t lx;
  53       EXTRACT_WORDS64 (lx, xlo);
  54       if ((hxs ^ lx) < 0 && (lx & 0x7fffffffffffffffLL) != 0)
  55         rhx--;
  56     }
  57   if (FIX_INT_FP_CONVERT_ZERO && rhx == 1023)
  58     return 0.0L;
  59   return (long double) (rhx - 1023);
  60 }
  61 #ifndef __logbl
  62 long_double_symbol (libm, __logbl, logbl);
  63 #endif